The invention relates to a diaphragm for a lung demand valve, in particular, although not exclusively, to a lung demand valve suitable for use in CBRN environments.
A lung demand valve (LDV) is typically used with breathing apparatus in order to control the supply of breathable gas to the user. An LDV usually comprises a flexible diaphragm that responds to pressure changes so as to control the flow of the breathable gas. A first side of the diaphragm is exposed to ambient pressure and the second side of the diaphragm is exposed to the pressure within the face-mask. The diaphragm is typically manufactured from an elastomer such as silicone.
If the LDV is to be used in chemical, biological, radiological and/or nuclear (CBRN) environments, it is necessary to prevent CBRN agents from being inhaled by the user. Since silicone is permeable, measures must be taken to ensure that CBRN agents cannot permeate through the diaphragm.
EP 1 575 675 A1 discloses a face-mask mechanically coupled to a LDV. The face-mask comprises a main mask and an inner mask which fits over the wearer's mouth and nose. The interior of the inner mask is in fluidic communication with the interior of the main mask by means of non-return valves. The interior of the main mask is in fluidic communication with an inlet port which is mechanically and fluidically coupled to a supply port of the LDV. The LDV includes a diaphragm and a cover which defines a passage through which exhaled air is used to flush the space around the diaphragm. Thus, any toxic or undesirable gas in the vicinity of the diaphragm is pushed out to the atmosphere by the exhaled air flowing past and around the diaphragm. This can prevent CBRN agents from accumulating on the outer surface of the diaphragm and permeating through the diaphragm.
EP 1 638 650 A1 discloses a LDV for use with breathing apparatus. The LDV has a valve assembly that includes an inlet for connection to a source of breathing gas, an outlet for connection to a face-mask to provide breathing gas to the user, and an actuator for controlling the flow of breathing gas between the inlet and the outlet in response to the user's respiration. The LDV further includes a flexible elastomeric diaphragm in operative connection with the actuator. The diaphragm is exposed to ambient pressure on a first side and exposed to a positive pressure within the face-mask on a second side. The regulator assembly also includes an impermeable and flexible shield that is spaced from the diaphragm and seals the first side of the diaphragm from certain toxic substances in the ambient atmosphere, while allowing the first side of the diaphragm to experience ambient pressure. The flexible shield moves along with the diaphragm during respiration without dampening the movement of the diaphragm during respiration of the user.
Whilst the above described arrangements may be appropriate in some circumstances, the complexity and therefore cost of the lung demand valve is increased when compared with a conventional lung demand valve.
It is therefore desirable to provide an improved arrangement.